Mixture of alicyclic polycarboxylic acid esters having high cis isomer content

ABSTRACT

The present invention relates to mixtures of alicyclic polycarboxylic esters with high cis content, to a process for their preparation by ring-hydrogenation of the corresponding aromatic polycarboxylic esters, and also to the use of the mixtures.

The present invention relates to mixtures of alicyclic polycarboxylicesters with high cis content, to a process for their preparation byring-hydrogenation of the corresponding aromatic polycarboxylic esters,and also to the use of the mixtures.

Alicyclic polycarboxylic esters, such as the esters ofcyclohexane-1,2-dicarboxylic acid, are used as a component oflubricating oil and as auxiliaries in metalworking. They are also usedas plasticizers for polyolefins.

For plasticizing PVC it is currently mainly esters of phthalic acid thatare used, for example dibutyl, dioctyl, dinonyl, or didecyl esters.Since these phthalates have recently been described as hazardous tohealth, there is a risk that their use in plastics could becomerestricted. Alicyclic polycarboxylic esters, some of which have beendescribed in the literature as plasticizers for various plastics, couldthen be available as suitable replacements, although with a somewhatdifferent performance profile.

The most economic route to preparation of alicyclic polycarboxylicesters in most cases is ring-hydrogenation of the corresponding aromaticpolycarboxylic esters, for example of the abovementioned phthalates.Some processes for this purpose have been disclosed:

U.S. Pat. No. 5,286,898 and U.S. Pat. No. 5,319,129 describe a processwhich can hydrogenate dimethyl terephthalate on supported Pd catalystsdoped with Ni or with Pt and/or with Ru, at temperatures of 140° C. orabove and at a pressure of from 50 to 170 bar, to give the correspondingdimethyl hexahydroterephthalate.

DE 28 23 165 hydrogenates aromatic carboxylic esters on supported Ni,Ru, Rh, and/or Pd catalysts to give the corresponding alicycliccarboxylic esters at from 70 to 250° C. and from 30 to 200 bar. U.S.Pat. No. 3,027,398 discloses the hydrogenation of dimethyl terephthalateon supported Ru catalysts at from 110 to 140° C. and from 35 to 105 bar.

WO 00/78704 discloses a process for hydrogenating benzenepolycarboxylicesters to give the corresponding alicyclic compounds. Here, use is madeof supported catalysts which comprise a metal of the 8th transitiongroup alone or together with at least one metal of the 1st or 7thtransition group of the Periodic Table and have 50% of macropores.Ruthenium is used as preferred metal of the 8th transition group.

The ring-hydrogenation of aromatic polycarboxylic esters can produce atleast two isomers with respect to the ring system and to the esterfunctions.

For example, the products from the hydrogenation of phthalic diesters(benzene-1,2-dicarboxylic diesters) are cis- and/ortrans-cyclohexane-1,2-dicarboxylic diesters. The cis diester here is theisomer in which one ester group has axial (a) orientation and the otherhas equatorial (e) orientation. The trans compound is the isomer inwhich both ester groups have either axial (a, a) or equatorial (e, e)orientation.

Hydrogenation of isophthalic diesters (benzene-1,3-dicarboxylicdiesters) can produce cis- and trans-cyclohexane-1,3-dicarboxylicdiesters. In the cis compound the ester groups have either axial-axial(a, a) or equatorial-equatorial (e, e) orientation. In the transcompound one ester group has axial orientation and the other hasequatorial orientation.

The hydrogenation of terephthalic diesters (benzene-1,4-dicarboxylicdiesters) can produce cis- and trans-cyclohexane-1,4-dicarboxylicdiesters. Here, in the cis compound one ester group has axialorientation and the other has equatorial orientation (a, e). In thetrans compound both ester groups have either axial (a, a) or equatorial(e, e) orientation.

In the case of alicyclic polycarboxylic esters having more than twosubstituents on the same ring system, each substituent can have cis ortrans configuration with respect to another substituent. For thepurposes of the present invention, all compounds in which the majorityof the ester groups have transconfiguration with respect to one anotherare to be regarded as trans compounds, irrespective of the otherconfigurations of the substituents with respect to one another.

The literature gives only sparse and incomplete information concerningthe configuration of the products which are produced during thering-hydrogenation of aromatic polycarboxylic esters.

For example, according to U.S. Pat. No. 3,027,165 the hydrogenation ofdimethyl terephthalate on a ruthenium catalyst produces a mixture ofdimethyl cis- and trans-cyclohexane-1,4-dicarboxylates with a meltingpoint below 20° C. It is known that the melting point of the transdiester is 70° C. and that the melting point of the cis diester is 7° C.Assuming conventional melting behavior (no mixed crystal formation),i.e. that starting from one pure isomer and adding the other isomer, themelting point of the mixture falls until the eutectic point has beenreached, it is possible to estimate that the hydrogenation mixture iscomposed mainly of dimethyl cis-cyclohexane-1,4-dicarboxylate.

S. Siegel and G. McCaleb in JACS, 81, 1959, pp. 3655-3658 describe thehydrogenation of dimethyl phthalates on suspended platinum oxide powderin glacial acetic acid. Irrespective of the pressure and concentration,the mixtures obtained of the corresponding cyclohexanoic acidderivatives have practically 100 mol % cis content. The yields of theesters isolated are not mentioned. This hydrogenation method has somedisadvantages: the catalyst has to be separated off from thehydrogenation mixture, and experience has shown that losses of catalystare unavoidable here. The solvent used, glacial acetic acid, is highlycorrosive and therefore requires apparatus made from high-performancematerials. In addition, the glacial acetic acid, which makes up from 80to 90% of the hydrogenation discharge, has to be separated off from thetarget product.

The preparation of dimethyl cyclohexanedicarboxylates with high ciscontent is therefore known. However, that publication does not disclosewhether other carboxylic esters with high cis content are alsoaccessible via the published method or any other method.

If the ruthenium-containing catalysts disclosed in WO 00/78704 are usedfor the hydrogenation of diisononyl phthalates, the product mixtureobtained has about 93 mol % of cis isomer and correspondingly 7 mol % ofthe trans isomer.

There are therefore no known alicyclic polycarboxylic ester mixtureswith above 93 mol % content of the cis isomer(s), with the exception ofmethyl cyclohexanedicarboxylates.

It was therefore an object of the present invention to prepare mixturesof this type and to test their use as plasticizers for plastics.

The invention therefore provides alicyclic polycarboxylic estermixtures, with the exception of methyl cyclohexanedicarboxylates,comprising at least two isomers with respect to the position of theester groups on the ring system, where the proportion of the cis isomersis above 93 mol %.

The mixtures of the invention are preferably prepared by hydrogenatingthe corresponding aromatic polycarboxylic esters. For this, use may bemade of a catalyst which comprises at least one precious metal of the8th transition group of the elements and comprises at least one metal ofthe 2nd transition group of the Periodic Table.

The present invention also provides a process for preparing alicyclicpolycarboxylic ester mixtures which have at least two isomers withrespect to the position of the ester groups on the ring system, andwhich have a proportion of the cis isomer above 93 mol %, by catalytichydrogenation of the corresponding aromatic polycarboxylic esters, wherethe catalyst comprises at least one precious metal of the 8th transitiongroup (ruthenium, rhodium, palladium, osmium, iridium, platinum), andcomprises at least one metal of the 2nd transition group of the PeriodicTable.

Among the abovementioned precious metals, preference is given toruthenium and very particularly to palladium. Zinc is used as preferredmetal of the 2nd transition group of the Periodic Table.

Besides the precious metals mentioned and zinc, any of the catalystsused in the process of the invention may also comprise inert supports,e.g. those composed of the metals aluminum, magnesium, titanium,zirconium, and/or silicon, in the form of oxide or mixed oxide. Thecatalysts may optionally also comprise salts of the support metalsmentioned, for example sulfates and/or phosphates. The catalysts usedaccording to the invention may also comprise processing aids or moldingauxiliaries, for example graphite.

The compositions given below are based on the reduced catalysts.

The precious metal content of the catalysts (calculated as metal) is inthe range from 0.1 to 10% by weight, in particular in the range from 0.5to 5% by weight, very particularly from 1 to 3% by weight.

The content (calculated as oxide) of metals of the 2nd transition group,e.g. zinc, in the catalysts is from 3 to 70% by weight, in particularfrom 10 to 50% by weight, very particularly from 20 to 30% by weight.

The process of the invention particularly preferably uses catalystswhich in reduced, active form comprise at least some of the preciousmetal in the oxidation state 0, and which preferably comprise zinc inthe oxidation state +2.

The catalysts are prepared by processes known per se, e.g. byprecipitation of carbonates, impregnation of previously preparedsupports, or mixing precursor compounds, and subsequent calcination.

The catalysts are advantageously converted into a form which has lowresistance to flow during the hydrogenation process, for exampletablets, cylinders, extrudates, or rings.

The process of the invention preferably carries out the hydrogenation inthe liquid phase. The hydrogenation may be carried out continuously orbatchwise on catalysts arranged in suspension or as pieces in a fixedbed. The process of the invention is preferably continuous hydrogenationof the catalyst arranged in a fixed bed, the product/starting materialphase being primarily liquid under the reaction conditions.

If the hydrogenation is carried out continuously on a catalyst arrangedin a fixed bed it is advantageous to convert the catalyst into theactive form prior to the hydrogenation process. This may be achieved byreducing the catalyst, using hydrogen-containing gases and a temperatureprogram. This reduction may, where appropriate, be carried out in thepresence of a liquid phase which trickles over the catalyst. The liquidphase used here may comprise a solvent or the hydrogenation product.

Various versions of the process of the invention may be selected. It maybe carried out under adiabatic, polytropic, or practically isothermalconditions, i.e. with a temperature rise which is typically less than10° C., in one or more stages. In the latter case it is possible for allof the reactors, advantageously tubular reactors, to be operated underadiabatic or practically isothermal conditions, or else for one or moreto be operated under adiabatic conditions and the others underpractically isothermal conditions. It is also possible for the aromaticpolycarboxylic esters to be hydrogenated in a straight pass or withproduct return.

The process of the invention is carried out in the mixed liquid/gasphase or liquid phase, concurrently in three-phase reactors, thehydrogenation gas being distributed in a manner known per se within theliquid starting material/product stream. To promote uniform liquiddistribution, improved dissipation of the heat of reaction, and highspace-time yield, the reactors are preferably operated with high liquidflow rates of from 15 to 120, in particular from 25 to 80, m³ per m² ofcross section of the empty reactor per hour. If a reactor is operatedwith a straight pass, the liquid hourly space velocity (LHSV) over thecatalyst may be from 0.1 to 10 h⁻¹.

The hydrogenation may be carried out in the absence, or preferably inthe presence, of a solvent. Solvents which may be used are any of theliquids which form a homogeneous solution with the starting material andproduct, exhibit inert behavior under hydrogenation conditions, and areeasy to remove from the product. The solvent may also be a mixture oftwo or more substances and, where appropriate, comprise water.

Examples of substances which may be used as solvents are the following:straight-chain or cyclic ethers, such as tetrahydrofuran or dioxane, andalso aliphatic alcohols whose alkyl radical has from 1 to 13 carbonatoms.

Alcohols which may preferably be used are isopropanol, n-butanol,isobutanol, n-pentanol, 2-ethylhexanol, nonanols, industrial nonanolmixtures, decanol, and industrial decanol mixtures, and tricedanols.

If alcohols are used as solvent it can be advantageous to use thealcohol or alcohol mixture which would be produced during saponificationof the product. This would exclude by-product formation viatransesterification. Another preferred solvent is the hydrogenationproduct itself.

By using a solvent it is possible to limit the concentration of aromaticcompounds in the reactor feed, and the result can be better temperaturecontrol achieved in the reactor. This can minimize side-reactions andtherefore increase product yield. The content of aromatic compounds inthe reactor feed is preferably from 1 to 35%, in particular from 5 to25%. In the case of reactors operated in loop mode, the desiredconcentration range can be adjusted via the circulation rate(quantitative ratio of returned hydrogenation discharge to startingmaterial).

The process of the invention is carried out in the pressure range from 3to 300 bar, in particular from 15 to 200 bar, very particularly from 50to 200 bar. The hydrogenation temperatures are from 50 to 220° C., inparticular from 100 to 200° C.

Hydrogenation gases which may be used are any desiredhydrogen-containing gas mixtures in which there are no detrimentalamounts present of catalyst poisons, such as carbon monoxide or hydrogensulfide. Examples of the inert gas constituents are nitrogen andmethane. It is preferable to use hydrogen at purity greater than 95%, inparticular greater than 98%.

The process of the invention can convert aromatic polycarboxylic acidsor derivatives of these, in particular their alkyl esters, to thecorresponding alicyclic polycarboxylic compounds. In the case of theesters here, both full esters and partial esters can be hydrogenated.Full esters are compounds in which all of the acid groups have beenesterified. Partial esters are compounds having at least one free acidgroup (or, where appropriate, one anhydride group) and at least oneester group.

The polycarboxylic esters of the invention and, respectively, thepolycarboxylic esters prepared by the process of the inventionpreferably contain 2, 3, or 4 ester functions.

The polycarboxylic esters preferably used in the process of theinvention are benzene-, diphenyl-, naphthalene- and/or anthracenepolycarboxylic esters. The resultant alicyclic polycarboxylic esters arecomposed of one or more C₆ rings, where appropriate linked by acarbon-carbon bond or fused.

Use may also optionally be made of polycarboxylic esters having anunderlying diphenyl oxide skeleton.

The alcohol component of the polycarboxylic esters is preferablycomposed of branched or unbranched alkyl, cycloalkyl, or alkoxyalkylgroups having from 1 to 25 carbon atoms. These may be identical ordifferent within one molecule of a polycarboxylic ester, i.e. they maycomprise identical or different isomers or identical or different chainlengths.

In one preferred embodiment, the present invention provides a processfor the hydrogenation of benzene-1,2-, -1,3-, or -1,4-dicarboxylicesters, and/or of benzene-1,2,3-, -1,2,4-, or -1,3,5-tricarboxylicesters, i.e. the mixtures of the invention comprise the isomers ofcyclohexane-1,2-, -1,3-, or -1,4-dicarboxylic esters, or ofcyclohexane-1,2,3-, -1,3,5-, or -1,2,4-tricarboxylic esters.

The following aromatic carboxylic acids may be used in the process ofthe invention:

-   naphthalene-1,2-dicarboxylic acid, naphthalene-1,3-dicarboxylic    acid, naphthalene-1,4-dicarboxylic acid,    naphthalene-1,5-dicarboxylic acid, naphthalene-1,6-dicarboxylic    acid, naphthalene-1,7-dicarboxylic acid,    naphthalene-1,8-dicarboxylic acid, phthalic acid    (benzene-1,2-dicarboxylic acid), isophthalic acid    (benzene-1,3-dicarboxylic acid), terephthalic acid    (benzene-1,4-dicarboxylic acid), benzene-1,2,3-tricarboxylic acid,    benzene-1,2,4-tricarboxylic acid (trimellitic acid),    benzene-1,3,5-tricarboxylic acid (trimesic acid),    benzene-1,2,3,4-tetracarboxylic acid. It is also possible to use    acids which are produced from the acids mentioned by using alkyl,    cycloalkyl, or alkoxyalkyl groups to substitute one or more of the    hydrogen atoms bonded to the aromatic core.

It is possible to use alkyl, cycloalkyl, or else alkoxyalkyl esters ofthe abovementioned acids, for example, these radicals encompassing,independently of one another, from 1 to 25, in particular from 3 to 15,very particularly from 8 to 13, particularly 9, carbon atoms. Theseradicals may be linear or branched. If a starting material has more thanone ester group, these radicals may be identical or different.

Examples of compounds which may be used in the process of the inventionas ester of an aromatic polycarboxylic acid are the following:

-   monomethyl terephthalate, dimethyl terephthalate, diethyl    terephthalate, di-n-propyl terephthalate, dibutyl terephthalate,    diisobutyl terephthalate, di-tert-butyl terephthalate, monoglycol    terephthalate, diglycol terephthalate, n-octyl terephthalate,    diisooctyl terephthalate, di-2-ethylhexyl terephthalate, di-n-nonyl    terephthalate, diisononyl terephthalate, di-n-decyl terephthalate,    di-n-undecyl terephthalate, diisodecyl terephthalate, diisododecyl    terephthalate, ditridecyl terephthalate, di-n-octadecyl    terephthalate, diisooctadecyl terephthalate, di-n-eicosyl    terephthalate, monocyclohexyl terephthalate, monomethyl phthalate,    dimethyl phthalate, di-n-propyl phthalate, di-n-butyl phthalate,    diisobutyl phthalate, di-tert-butyl phthalate, monoglycol phthalate,    diglycol phthalate, di-n-octyl phthalate, diisooctyl phthalate,    di-2-ethylhexyl phthalate, di-n-nonyl phthalate, diisononyl    phthalate, di-n-decyl phthalate, di-2-propylheptyl phthalate,    diisodecyl phthalate, di-n-undecyl phthalate, diisoundecyl    phthalate, ditridecyl phthalate, di-n-octadecyl phthalate,    diisooctadecyl phthalate, di-n-eicosyl phthalate, monocyclohexyl    phthalate, dicyclohexyl phthalate, monomethyl isophthalate, dimethyl    isophthalate, diethyl isophthalate, di-n-propyl isophthalate,    di-n-butyl isophthalate, diisobutyl isophthalate, di-tert-butyl    isophthalate, monoglycol isophthalate, diglycol isophthalate,    di-n-octyl isophthalate, diisooctyl isophthalate, 2-ethylhexyl    isophthalate, di-n-nonyl isophthalate, diisononyl isophthalate,    di-n-decyl isophthalate, diisodecyl isophthalate, di-n-undecyl    isophthalate, diisododecyl isophthalate, di-n-dodecyl isophthalate,    ditridecyl isophthalate, di-n-octadecyl isophthalate, diisooctadecyl    isophthalate, di-n-eicosyl isophthalate, monocyclohexyl    isophthalate.

It is also possible to use mixtures made from two or more polycarboxylicesters. Mixtures of this type may be obtained in the following ways, forexample:

-   a) a polycarboxylic acid is partially esterified using an alcohol in    such a way as to give both full and partial esters.-   b) A mixture of at least two polycarboxylic acids is esterified    using an alcohol, producing a mixture of at least two full esters.-   c) A polycarboxylic acid is treated with an alcohol mixture, and the    product can be a mixture of many full esters.-   d) A polycarboxylic acid may also be partially esterified using an    alcohol mixture.-   e) A mixture of at least two carboxylic acids may also be partially    esterified using an alcohol mixture.-   f) A mixture of at least two polycarboxylic acids may also be    partially esterified using an alcohol mixture.

Instead of the polycarboxylic acids in reactions a) to f), use may alsobe made of their anhydrides.

Aromatic esters are often prepared industrially from alcohol mixtures,in particular the full esters by route c).

Examples of corresponding alcohol mixtures are:

C₅ alcohol mixtures prepared from linear butenes by hydroformylationfollowed by hydrogenation;

C₅ alcohol mixtures prepared from butene mixtures which comprise linearbutene and isobutene, by hydroformylation followed by hydrogenation;

C₆ alcohol mixtures prepared from a pentene or from a mixture of two ormore pentenes, by hydroformylation followed by hydrogenation;

C₇ alcohol mixtures prepared from triethylene or dipropene or from ahexeneisomer or from some other mixture of hexeneisomers, byhydroformylation followed by hydrogenation;

C₈ alcohol mixtures, such as 2-ethylhexanol (2 isomers), prepared byaldol condensation of n-butyraldehyde followed by hydrogenation;

C₉ alcohol mixtures prepared from C₄ olefins by dimerization,hydroformylation, and hydrogenation. The starting materials here forpreparing the C₉ alcohols may be isobutene or a mixture of linearbutenes or mixtures of linear butenes and isobutene. The C₄ olefins maybe dimerized with the aid of various catalysts, such as protonic acids,zeolites, organometallic nickel compounds, or solid nickel-containingcatalysts. The C₈ olefin mixtures may be hydroformylated with the aid ofrhodium catalysts or cobalt catalysts. There is therefore a wide varietyof industrial C₉ alcohol mixtures.C₁₀ alcohol mixtures prepared from tripropylene by hydroformylationfollowed by hydrogenation; 2-propylheptanol (2 isomers) prepared byaldol condensation of valeraldehyde followed by hydrogenation;C₁₀ alcohol mixtures prepared from a mixture of at least two C₅aldehydes by aldol condensation followed by hydrogenation;C₁₃ alcohol mixtures prepared from hexaethylene, tetrapropylene, ortributene, by hydroformylation followed by hydrogenation.

Other alcohol mixtures may be obtained by hydroformylation followed byhydrogenation from olefins or olefin mixtures which arise inFischer-Tropsch syntheses, in the dehydrogenation of hydrocarbons, inmetathesis reactions, in the polygas process, or in other industrialprocesses, for example.

Olefin mixtures with olefins of differing carbon numbers may also beused to prepare alcohol mixtures.

The process of the invention can use any ester mixture prepared fromaromatic polycarboxylic acids and from the abovementioned alcoholmixtures. According to the invention, preference is given to estersprepared from phthalic acid or phthalic anhydride and from a mixture ofisomeric alcohols having from 6 to 13 carbon atoms.

Examples of industrial phthalates which can be used in the process ofthe invention are products with the following tradenames:

Vestinol C (di-n-butyl phthalate) (CAS No. 84-74-2); Vestinol IB(diisobutyl phthalate) (CAS No. 84-69-5); Jayflex DINP (CAS No.68515-48-0); Jayflex DIDP (CAS No. 68515-49-1); Palatinol 9P(68515-45-7), Vestinol 9 (CAS No. 28553-12-0); TOTM (CAS No. 3319-31-1);Linplast 68-TM, Palatinol N (CAS No. 28553-12-0); Jayflex DHP (CAS No.68515-50-4); Jayflex DIOP (CAS No. 27554-26-3); Jayflex UDP (CAS No.68515-47-9); Jayflex DIUP (CAS No. 85507-79-5); Jayflex DTDP (CAS No.68515-47-9); Jayflex L9P (CAS No. 68515-45-7); Jayflex L911P (CAS No.68515-43-5); Jayflex L11P (CAS No. 3648-20-2); Witamol 110 (CAS No.68515-51-5); Witamol 118 (Di-n-C8-C10-alkyl phthalate) (CAS No.71662-46-9); Unimoll BB (CAS No. 85-68-7); Linplast 1012 BP (CAS No.90193-92-3); Linplast 13XP (CAS No. 27253-26-5); Linplast 610P (CAS No.68515-51-5); Linplast 68 FP (CAS No. 68648-93-1); Linplast 812 HP (CASNo. 70693-30-0); Palatinol AH (CAS No. 117-81-7); Palatinol 711 (CAS No.68515-42-4); Palatinol 911 (CAS No. 68515-43-5); Palatinol 11 (CAS No.3648-20-2); Palatinol Z (CAS No. 26761-40-0); Palatinol DIPP (CAS No.84777-06-0); Jayflex 77 (CAS No. 71888-89-6); Palatinol 10 P (CAS No.533-54-0); Vestinol AH (CAS No. 117-81-7).

Reference is made below to the possible stereoisomers of the alicyclicsystem, the trans form being differentiated from the cis form. Forexample, as mentioned above, in the case of cyclohexane-1,2-dicarbocylicesters the trans forms are the compounds in which the ester groups haveeither axial-axial (a,a) or equatorial-equatorial (e,e) orientation. Inthe cis compounds one ester group has axial (a) orientation and theother has equatorial (e) orientation. As stated above, otherorientations may apply for distinguishing between these two forms in thecase of other alicyclic polycarboxylic esters.

In particular versions of the process of the invention, dinonylphthalates or a mixture of isomeric dinonyl phthalates is/arehydrogenated to give a mixture of isomeric dinonylcyclohexane-1,2-dicarboxylates, the proportion of the cis isomer withrespect to the position of the carboxy groups on the cyclohexane ringbeing above 93 mol %.

Similarly, di(2-ethylhexyl) phthalates may be reacted to givedi(2-ethylhexyl)cyclohexane-1,2-dicarboxylates, or didecyl phthalatesmay be reacted to give didecyl cyclohexane-1,2-dicarboxylates. Withrespect to the cis/trans isomers, what has been said for the isononylester is again applicable.

The mixtures of the invention or mixtures prepared according to theinvention comprise above 93 mol %, based on the entire amount of ester,of cis compound(s). The mixtures preferably comprise from 94 to 100 mol%, from 95 to 100 mol %, from 96 to 100 mol %, from 97 to 100 mol %,from 98 to 100 mol %, or from 99 to 100 mol %, of the cis isomer(s).

The present invention also provides the use of the alicyclicpolycarboxylic esters of the invention or prepared according to theinvention as a plasticizer in plastics. Preferred plastics are PVC,homo- and copolymers based on ethylene, on propylene, on butadiene, onvinyl acetate, on glycidyl acrylate, on glycidyl methacrylate, onacrylates, or on acrylates having, bonded to the oxygen atom of theester group, alkyl radicals of branched or unbranched alcohols havingfrom one to ten carbon atoms, or on styrene or on acrylonitrile, andhomo- or copolymers of cyclic olefins. The following plastics may bementioned as representatives of the above groups:

polyacrylates having identical or different alkyl radicals having from 4to 8 carbon atoms, bonded to the oxygen atom of the ester group, inparticular having the n-butyl, n-hexyl, n-octyl, or 2-ethylhexylradical, polymethacrylate, polymethyl methacrylate, methylacrylate-butyl acrylate copolymers, methyl methacrylate-butylmethacrylate copolymers, ethylene-vinyl acetate copolymers, chlorinatedpolyethylene, nitrile rubber, acrylonitrile-butadiene-styrenecopolymers, ethylene-propylene copolymers, ethylene-propylene-dienecopolymers, styrene-acrylonitrile copolymers, acrylonitrile-butadienerubber, styrene-butadiene elastomers, and methylmethacrylate-styrene-butadiene copolymers.

The alicyclic polycarboxylic esters of the invention may moreover beused to modify plastics mixtures, for example the mixture of apolyolefin with a polyamide.

The present invention also provides mixtures made from plastics with thealicyclic polycarboxylic esters of the invention, or prepared accordingto the invention. Suitable plastics are the abovementioned compounds.These mixtures preferably comprise at least 5% by weight, particularlypreferably from 20 to 80% by weight, very particularly preferably from30 to 70% by weight, of the alicyclic polycarboxylic esters.

Mixtures made from plastics, in particular PVC, and comprising one ormore of the alicyclic polycarboxylic esters of the invention, may bepresent in the following products, for example:

casings for electrical devices, such as kitchen appliances, computercases, casings and components of phonographic and television equipment,of piping, of apparatus, of cables, of wire sheathing, of insulatingtapes, of window profiles, in interior decoration, in vehicleconstruction and furniture construction, plastisols, in floor coverings,medical products, packaging for food or drink, gaskets, films, compositefilms, phonographic disks, synthetic leather, toys, containers forpackaging, adhesive-tape films, clothing, coatings, and fibers forfabrics.

Mixtures made from plastics, in particular PVC, and comprising one ormore of the alicyclic polycarboxylic esters of the invention maymoreover be used for producing the following products, for example:

a casing for electrical devices, piping, apparatus, a cable, wiresheathing, a window profile, a floor covering, a medical product, a toy,packaging for food or drink, a gasket, a film, a composite film, aphonographic disk, synthetic leather, a container for packaging, anadhesive-tape film, clothing, a coating, or a fiber for fabrics.

Besides the abovementioned applications, the alicyclic polycarboxylicesters of the invention may be used as a component in lubricating oil,or as a constituent of coolants or metal working fluids.

The examples below are intended to illustrate the invention withoutrestricting the scope of protection defined by the patent claims.

Analysis:

The ratio of cis- and trans-cyclohexane-1,2-dicarboxylic diesters wasdetermined by ¹H NMR spectroscopy.

-   Measuring device: Avance DPX-360 NMR spectrometer from the company    Bruker-   Measurement frequency: 360 MHz-   Sample head: QNP sample head, 5 mm-   Solvent: CDCl₃ (degree of deuteration 99.8%)-   Standard: Tetramethylsilane (TMS)-   Measurement temperature: 303 K-   Number of scans: 32-   Delay: 1 s-   Acquisition time: 4.4 s-   Spectral width: 7440.5 Hz-   Pulse angle: 30°-   Pulse length: 3.2 μs

An example of the method of recording the ¹H NMR spectra compriseddissolving about 20 mg of the specimen in about 0.6 ml of CDCl₃ (with 1%by weight of TMS). The spectra were recorded under the conditions givenabove and referenced to TMS=0 ppm.

In the ¹H NMR spectra obtained, the methyne signals for dialkyl cis- andtrans-hexahydrophthalates could be distinguished with chemical shifts ofabout 2.8 ppm and 2.6 ppm, respectively, the signal shifted toward lowerfield corresponding to the cis compound (larger ppm value). To quantifythe isomers, the integrals were determined from 3.0 ppm to 2.7(2) ppmand from 2.7(2) ppm to 2.5 ppm, the two integrals being separated in themiddle between the signals. The ratio of the two isomeric structurescould be determined from the intensity ratios.

EXAMPLE 1 Comparative Example

The catalyst used comprised catalyst H 14184 (0.5% of Ag on transitionalumina in the form of extrudates of diameter 1.2 mm) from Degussa. 57 gof catalyst were placed in a rotating basket in a stirred autoclave andreduced in accordance with the manufacturer's instruction in hydrogen at4 bar and 200° C. The autoclave was then filled with 600 g of diisononylphthalate (abbreviated to DINP, the product Vestinol 9 from Oxeno GmbH),and hydrogen was applied at a pressure of 200 bar. Hydrogenation wasthen carried out at a temperature of 120° C. for 70 hours. DINPconversion was complete. The proportion of diisononylcis-cyclohexanedicarboxylate (cis-DINCH) in the product was found to be85%, the remainder being trans-DINCH.

EXAMPLE 2 Comparative Example

The experiment of example 1 was repeated, except that in this thereaction temperature was raised to 200° C. and the hydrogenation timeshortened to 21.2 h. Conversion was again complete, but this time thecis-DINCH content was only 81.4%. Although the very high reactiontemperature achieved a high reaction rate, isomeric selectivity reducedmarkedly.

EXAMPLE 3 Inventive

The catalyst used comprised catalyst H 14184 (0.5% of Pd on transitionalumina in the form of extrudates of diameter 1.2 mm) from Degussa AG,which had also been doped with 2% ZnO. 59 g of catalyst were placed in arotating basket in a stirred autoclave and reduced in accordance withthe manufacturer's instruction in hydrogen at 4 bar and 200° C. Theautoclave was then filled with 600 g of diisononyl phthalate(abbreviated to DINP, the product Vestinol 9 from Oxeno GmbH), andhydrogen was applied at a pressure of 200 bar. Hydrogenation was thencarried out at a temperature of 120° C. for 60 hours. DINP conversionwas complete. The proportion of diisononyl cis-cyclohexanedicarboxylate(cis-DINCH) in the product was found to be 97.2%, the remainder beingtrans-DINCH.

EXAMPLE 4 Comparative Example

The catalyst used comprised 1.0% of Ru on □-Al₂O₃ in the form of beadsof diameter 3 mm. 74 g of catalyst were placed in a rotating basket in astirred autoclave and reduced in accordance with the manufacturer'sinstruction in hydrogen at 4 bar and 200° C. The autoclave was thenfilled with 600 g of diisononyl phthalate (abbreviated to DINP, theproduct Vestinol 9 from Oxeno GmbH), and hydrogen was applied at apressure of 200 bar. Hydrogenation was then carried out at a temperatureof 120° C. for 22 hours. DINP conversion was complete. The proportion ofdiisononyl cis-cyclohexanedicarboxylate (cis-DINCH) in the product wasfound to be 93.6%, the remainder being trans-DINCH.

EXAMPLE 5 Inventive

The experiment of example 4 was repeated under the same conditions,except that in this case use was made of a catalyst which had also beendoped with 2.5% of ZnO. Conversion was again complete, and cis-DINCHcontent was 97.3%.

1. A process for preparing alicyclic polycarboxylic acid ester isomermixtures, which comprises: hydrogenating an aromatic polycarboxylic acidester isomer in the presence of catalyst which comprises at least oneprecious metal of the 8^(th) transition Group and at least one metal ofthe 2nd transition Group of the Periodic Table, wherein the alicyclicpolycarboxylic acid ester isomer mixture produced comprises above 93 mol% amount of the cis isomer.
 2. The process as claimed in claim 1,wherein the hydrogenation is conducted at a temperature ranging from 50to 220° C. and at a pressure ranging from 3 to 300 bar.
 3. The processas claimed in claim 1, wherein the aromatic polycarboxylic acid estersare benzene- or biphenylpolycarboxylic acid esters, diphenyl oxidepolycarboxylic esters, or naphthalene- or anthracenepolycarboxylic acidesters.
 4. The process as claimed in claim 1, wherein the polycarboxylicacid esters have 2, 3 or 4 ester groups.
 5. The process as claimed inclaim 1, wherein the alcohol components of the polycarboxylic acidesters are alkoxyalkyl, cycloalkyl, and/or alkyl groups having from 1 to25 carbon atoms, branched or unbranched, and in each instance identicalor different.